At the lateral border of the 1st rib as the continuation of the subclavian artery and ends at the inferior border of the teres major. It passes posterior to the pectoralis minor into the arm and becomes the brachial artery when it passes the inferior border of the teres major, at which point it usually reached the humerus.

How many parts is the axillary artery divided into?

3

Where does the axilla end?

The inferior border of the teres major

First part of the axillary artery

1st part is between the lateral border of the first rib and the medial border of the pectoralis minor.

What does the axillary artery become and when?

Brachial artery when it passes the inferior border of teres major, at which point it usually has reached the humerus.

The Second part of the axillary artery

Lies posterior to pectoralis minor and has two branches--the thoracoacromial and lateral thoracic arteries--which pass medial and lateral to the muscle, respectively.

The third part of the axillary artery

Extends from the lateral border of pectoralis minor to the inferior border of teres major and has three branches.
Subscapular artery
Anterior circumflex humeral
Posterior circumflex humeral